Device and method for monitoring operation of a flash memory

ABSTRACT

A flash memory device includes an array of memory cells for storing data pages, at least one buffer (e.g. a memory buffer and a cache buffer) for transferring the data pages to and from the array of memory cells and a host, and an output pin. A logic mechanism is operative to select, from among a plurality of conditions related to an operation on the array of memory cells, a condition that drives a signal being output on the output pin. A data page transfer by the host is contingent on the signal being output on the output pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application No. 60/734,708, filed Nov. 9, 2005.

FIELD OF THE INVENTION

The present invention relates generally to a method for efficiently monitoring operation of a flash memory device.

BACKGROUND OF THE INVENTION

Flash memory devices have been known for many years. Standard flash memory devices known in the art store data in a memory array, arranged in groups, called pages and/or blocks.

An example of a NAND flash memory device known in the art is Samsung Electronics device No. K9K4G08U1M. The Data Sheet (herein under—DS) of this device is incorporated by reference for all purposes as if fully set forth herein.

When exchanging data with a flash memory, an entire data page is usually written to the memory array or read out of it simultaneously, within one operation, from/to an internal buffer (or register) called a page buffer. A Host device, which the flash memory device is connected to, transfers the data to/from this page buffer.

The process of reading data from the flash memory device is carried out in two phases. In the first phase, data is transferred from the memory array to the page buffer of the flash memory device. In the second phase, data is transferred from the page buffer to the Host device.

The process of writing data to the flash memory device is carried out in two phases as well, such that in the first phase data is transferred from the Host device to the page buffer of the flash memory device and in the second phase data is transferred from the page buffer to the memory array.

Data transfer between the Host device and the page buffer is controlled by the Host device's hardware and/or software modules, and so the start and finish of this data transfer is directly controlled by these modules. However, the data transfer between the page buffer and the memory array is usually performed autonomously by the flash memory device, without intervention of the Host device. Therefore, the Host device's hardware and/or software modules are not aware of such transfer timing.

Because the data transfer between the page buffer and the memory array is time consuming (this phase lasts between tens to hundreds of microseconds), a special notification of a busy memory array is provided to the Host device. This notification is implemented as a “Ready/Busy” hardware signal, produced by the flash memory device and monitored by the Host device.

On top of the implementation of a hardware signal, the above mentioned notification of a busy memory array may further be available to the Host device software within status information via a “status register”.

For example, the hardware signal may generate an interrupt to the Host device upon completion of an operation, indicating that the flash memory device is ready for executing a new operation or, alternatively, the Host device's software module may poll the memory status register, waiting for this event.

The time spent for data exchange between the Host device and the flash memory device includes both Host ⇄ Buffer and Buffer ⇄ Memory Array transfer periods. As the data page size of existing flash memory devices increases, the Host ⇄ Buffer transfer time increases as well, and becomes comparable to the Buffer ⇄ Memory Array transfer time. For example, in a NAND flash memory device known in the art having a 2 KByte data page, the Host ⇄ Buffer transfer time is typically 50 to 100 microseconds per page, while Buffer ← Memory Array page read time is 20 to 50 microseconds per page and Buffer → Memory Array page program (write) time is 200 to 800 microseconds per page.

Therefore, in order to increase the system's throughput, some flash memory devices include an additional data buffer —a cache buffer for enabling a simultaneous data transfer between the Host device and this cache buffer and between the page buffer and the memory array.

It should be noted, that the NAND flash memory device whose data sheet is incorporated by reference herein implements a cache buffer for page programming only, however, there are other devices, which use it for a read operation as well.

In order to provide the Host device with the necessary transfer timing information and to achieve time efficiency, existing flash memory devices which include such a cache buffer include two logical “Ready/Busy” indications. The first indication, defined “Cache Ready/Busy” (or just “Ready/Busy”), is for indicating the availability of the cache buffer regarding the data transfer. The second indication, defined “True Ready/Busy”, is for indicating the current state of the memory array.

Practically, Host devices need to use both indications. While the “Cache Ready/Busy” indication is used to trigger next data transfer in a series, the “True Ready/Busy” indication is used to indicate whether the current operation running in the flash memory device has finished, the memory array is free, and a different operation may be started. This may happen when there is a need to switch from page read to page program or vice versa, or when the application needs to know that the current page programming indeed finished (page data is in the memory array, not only in a buffer) and next step in the application may start.

However, in flash memory devices known in the art only the “Cache Ready/Busy” indication is handled in a “hardware manner” (i.e. provided as a hardware “Ready/Busy” signal), by generating an interrupt to the application, as an example, whereas the “True Ready/Busy” indication is only polled by the Host device's software module, thus increasing the complexity of this module and decreasing its flexibility and time-efficiency.

One option to handle this situation is to implement the two logical “Ready/Busy” indications to be output by the flash memory device as hardware signals.

However, such an approach is impractical, because it violates the standard NAND flash interface and introduces lack of compatibility to similar devices which do not include a cache.

Existing methods for monitoring operation of flash memory devices do not implement the two logical “Ready/Busy” indications in a “hardware” manner.

There is thus a widely recognized need for, and it would be highly advantageous to have, a flash memory device and method for monitoring operation of the flash memory device, which is an alternative approach to prior art techniques, such that the flash memory device is compliant to a standard NAND flash interface.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention to disclose an alternative method to prior art techniques used for monitoring operation of a flash memory device.

The present invention is an innovative flash memory device and method for monitoring operation of the flash memory device, while providing two logical “Ready/Busy” indications implemented in a “hardware” manner as a single hardware signal, such that the flash memory device is compliant to a standard NAND flash interface.

The flash memory device of the present invention includes a logic mechanism that is operative to change the logical meaning of a signal (i.e. the condition that invokes the signal) being output on an output pin between a plurality of signals according to a request asserted from a Host.

In accordance with the present invention, there is provided a flash memory device including: (a) an array of memory cells for storing data pages; (b) at least one buffer for transferring the data pages to and from the array of memory cells and a host; (c) an output pin; and (d) a logic mechanism that is operative to select, from among a plurality of conditions related to an operation on the array of memory cells, a condition that drives a signal being output on the output pin.

Preferably, the condition that drives the signal being output on the output pin is that the array of memory cells is busy (i.e. the array of memory cells is engaged in being addressed for reading, programming, updating, erasing, etc.) or that one buffer is busy (i.e. the memory buffer is engaged in being addressed for reading, programming, updating, erasing, etc.). Preferably, the condition is a compound condition (i.e. a Boolean combination of two other conditions), for example—that the array of memory cells is busy and that one buffer (e.g. the memory buffer) is busy, the array of memory cells is busy or the memory buffer is busy, the array of memory cells is not busy and the memory buffer is busy, the array of memory cells is not busy or the memory buffer is busy, the array of memory cells is busy and the memory buffer is not busy, the array of memory cells is busy or the memory buffer is not busy, the array of memory cells is not busy and the memory buffer is not busy, the array of memory cells is not busy or the memory buffer is not busy.

Optionally, the condition that invokes the signal being output on the output pin is a failure of an operation.

Optionally, the condition that invokes the signal being output on the output pin may be a logical operational state, such as a page program failure, a block erase failure, etc.

Preferably, the logic mechanism selects the condition according to at least one command received from a host. Alternatively, the command operates the logic mechanism to toggle the condition each time the command is received. Also preferably, the change persists until the flash memory device receives a reset command or until the flash memory device is powered up. Obviously, the command is also overridden by a subsequent command even without a reset command or a power up. Also preferably, the change persists for only one write/erase operation before returning to operate in default mode. Also preferably, the logic mechanism selects the condition according the command received from the host, such that each command corresponds to a different respective condition (e.g. set by a respective parameter).

In accordance with the present invention, there is further provided a method for monitoring operation of a flash memory device, the method including the steps of: (a) sending a command to the flash memory device instructing the flash memory device to select a condition, from among a plurality of conditions, under which a state of an output pin changes; and (b) interrogating the condition by sensing the changed state of the output pin.

Preferably, a data page transfer by the host is contingent on the interrogation of the selected condition.

Preferably, the condition is that an array of memory cells is busy, that a buffer (e.g. a memory buffer) is busy or a compound condition (for example, that the array of memory cells is (is not) busy and/or that the memory buffer is (is not) busy).

Preferably, the condition is a failure of an operation.

Preferably, the condition that invokes the signal being output on the output pin may be a logical operational state, such as a page program failure, a block erase failure, etc.

Additional features and advantages of the invention will become apparent from the following drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention with regard to the embodiment thereof, reference is made to the accompanying drawing, in which like numerals designate corresponding sections or elements throughout, and in which:

The SOLE FIGURE is a block diagram of the preferred flash memory device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is an innovative flash memory device and method for monitoring operation of the flash memory device, while providing two logical “Ready/Busy” indications implemented in a “hardware” manner as a single hardware signal, such that the flash memory device is compliant to a standard NAND flash interface.

The flash memory device of the present invention includes a logic mechanism that is operative to select, optionally by a request asserted from a Host, a condition that drives a signal being output on an output pin. The condition is selected from among a plurality of conditions that are related to an operation on an array of memory cells being a busy condition after an operation or a failure indication after an operation, as an example.

As an example for usage of such a “Ready/Busy” indication, the hardware signal may be an interrupt to the Host upon completion of an operation, indicating that the flash memory device is ready for a new operation or, alternatively, the Host may poll the memory status register for a change of status.

The flash memory device of the present invention is equally applicable to assert a hardware signal providing a “Cache Ready/Busy” indication solely, a “True Ready/Busy” indication solely or both “Cache Ready/Busy” and “True Ready/Busy” indications. The flash memory device may further select a condition that is compound condition (i.e. a Boolean combination of two other conditions), such as—that the array of memory cells is busy and that the memory buffer is busy, the array of memory cells is busy or the memory buffer is busy, the array of memory cells is not busy and the memory buffer is busy, the array of memory cells is not busy or the memory buffer is busy, the array of memory cells is busy and the memory buffer is not busy, the array of memory cells is busy or the memory buffer is not busy, the array of memory cells is not busy and the memory buffer is not busy, the array of memory cells is not busy or the memory buffer is not busy.) Referring now to FIG. 1, there is shown a block diagram of the preferred flash memory device 10 of the present invention. Flash memory device 10 includes a memory array 12 of memory cells C1 to Cn for storing data pages. A Host device 20, which the flash memory device is connected to, transfers the data pages via Data signals 36 to/from an Input/Output (I/O) Interface unit 34.

An entire data page is written to the memory array or read out of it from/to the Page Buffer 16. Flash memory device 10 includes an additional data buffer—a Cache Buffer 18 for enabling a simultaneous data transfer between the Host device 20 and the Cache Buffer 18 and between the Page Buffer 16 and the memory array 12. The simultaneous data transfer increases the overall throughput of the flash memory device 10.

A Logic Mechanism 22 is operative to change the meaning of a RDY/ BSY signal 26 being output from a RDY BSY Selector 24. Logic Mechanism 22 transfers a select signal 40 for selecting between a “True Ready/Busy” signal 28 and a “Cache Ready/Busy” signal 30. The functionality of the select signal 40 is set according to a command asserted from the Host device 20 via Control signals 38 and Data signals 36.

Status information, such as the two logical “True Ready/Busy” and “Cache Ready/Busy” indications, is further provided to the Host device 20 from a Memory Status register 32 connected to the Logic Mechanism 22. The status information is transferred from the Memory Status register 32 to the Host device 20 via the Input/Output (I/O) Interface unit 34.

In some preferred embodiments of the present invention the command asserted from the Host device 20 for changing the meaning of the RDY/ BSY signal 26 operates the Logic Mechanism 22 as follows:

In one preferred embodiment there is implemented a command which toggles the meaning of the “Ready/Busy” signal each time the Host device issues this command.

In another preferred embodiment, there is provided a pair of commands, such that each command sets the RDY/ BSY signal 26 a different meaning.

In a third preferred embodiment, there is provided a command including a corresponding parameter, such that the meaning of the RDY/ BSY signal 26 is explicitly stated according to the parameter.

In a fourth preferred embodiment, there is provided a command which operates the Logic Mechanism 22 to change the meaning of the RDY/ BSY signal 26 to a non-default state until a reset command or a power up event is encountered.

In a fifth preferred embodiment, there is provided a command which operates the Logic Mechanism 22 to change the meaning of the RDY/ BSY signal 26 until the transition from a “Busy” state to a “Ready” state occurs (following such a transition, an automatic return to a previous state occurs).

The present invention is described herein as providing the two logical “Cache Ready/Busy” and “True Ready/Busy” indications. However, the present invention is not limited to these two logical indications only, and is equally applicable for indication of other logical operational states within a memory device provided in a similar manner (e.g. page program failure, block erase failure, etc.).

It should be noted that the present invention relates to a NAND flash memory device. However, it can be understood that other implementations are possible within the scope of the invention, thus relating to any device and method for monitoring operation of a flash memory device.

Having described the invention with regard to a certain specific embodiment thereof, it is to be understood that the description is not meant as a limitation, since further modifications will now suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims. 

1. A flash memory device comprising: (a) an array of memory cells for storing data pages; (b) at least one buffer for transferring said data pages between said array of memory cells and a host; (c) an output pin; and (d) a logic mechanism that is operative to select, from among a plurality of conditions related to an operation on said array of memory cells, a condition that drives a signal being output on said output pin.
 2. The flash memory device of claim 1, wherein said selected condition is that said array of memory cells is busy.
 3. The flash memory device of claim 1, wherein said selected condition is that one buffer of said at least one buffer is busy.
 4. The flash memory device of claim 1, wherein said selected condition is a compound condition.
 5. The flash memory device of claim 1, wherein said selected condition is a failure of an operation.
 6. The flash memory device of claim 1, wherein said selected condition is a logical operational state selected from the group consisting of: a page program failure and a block erase failure.
 7. The flash memory device of claim 1, wherein said logic mechanism selects said condition according to at least one command received from said host.
 8. The flash memory device of claim 7, wherein said at least one command operates said logic mechanism to toggle said condition each time said at least one command is received.
 9. The flash memory device of claim 7, wherein said logic mechanism maintains said selection until an event selected from the group consisting of: a reset command and a powering up is encountered.
 10. The flash memory device of claim 7, wherein said logic mechanism maintains said selection during an activation of only a single command.
 11. The flash memory device of claim 7, wherein said logic mechanism selects said condition according to said at least one command received from said host, each of said at least one command corresponding to a different respective condition.
 12. A method for monitoring operation of a flash memory device, the method comprising the steps of: (a) sending a command to the flash memory device instructing the flash memory device to select a condition, from among a plurality of conditions, under which a state of an output pin changes; and (b) interrogating said selected condition by sensing said changed state of said output pin.
 13. The method of claim 12, wherein said interrogation of said selected condition contingents a data page transfer.
 14. The method of claim 12, wherein said selected condition is that an array of memory cells is busy.
 15. The method of claim 12, wherein said selected condition is that a buffer is busy.
 16. The method claim 12, wherein said selected condition is a compound condition.
 17. The method of claim 12, wherein said selected condition is a failure of an operation.
 18. The method of claim 12, wherein said selected condition is a logical operational state selected from the group consisting of: a page program failure and a block erase failure. 